Thermoplastic elastomer gels are materials characterized by very low hardness, elastic behaviour, that is to say they regain their initial shape after a deformation, even a large-amplitude deformation, and a softening point above which they become plastic, which facilitates their processing.
Such gels may especially have, as a matrix, thermoplastic elastomers (TPE) and in particular styrene thermoplastic elastomers (known as TPSs), such as styrene/butadiene (SB), styrene/isoprene (SI), styrene/isobutylene (SIB), styrene/ethylene/propylene (SEP), styrene/ethylene/butylene (SEB) block copolymers, or else, styrene/butadiene/styrene (SBS), styrene/isoprene/styrene (SIS), styrene/butadiene/isoprene/styrene (SBIS), styrene/isobutylene/styrene (SIBS), styrene/ethylene/butylene/styrene (SEBS), styrene/ethylene/propylene/styrene (SEPS) and styrene/ethylene/ethylene/propylene/styrene (SEEPS) block copolymers, and blends of these copolymers.
In order to obtain a very low hardness, these gels also comprise a high proportion of extender oils. As a general rule, the extender oil is introduced into these gels in a proportion of 200 phr (per hundred of elastomer by weight) or more.
However, the storage, handling and preparation of these gels, with a view to the conversion thereof, presents specific difficulties. More particularly, the problem arises when it is desired to form small-sized granulates or pellets for feeding conventional means for converting thermoplastics.
It is known from the prior art to coat these products with anti-tack agents in order to prevent them from agglomerating during these industrial phases.
Conventionally, the anti-tack agents are chosen from finely divided materials such as silica, talc, mica, zinc oxide or zinc stearate. These agents may be used in the pure state or in the form of a mixture in which there is a majority proportion, of greater than 80%, of one of the above anti-tack agents.
The anti-tack agents may be deposited on the surface of the pellets or granulates of thermoplastic gels, by contacting with a powder, by spraying with a solution or by dip-coating in a liquid formed of a suspension having a high concentration of the anti-tack agent in question.
The problem faced by the use of anti-tack agents of any nature, lies in the fact that these products, when they are present above a certain proportion, substantially modify the properties of the thermoplastic gels such as, for example, the elastic modulus or the elongation capacity. Therefore, particular attention is needed when it is desired to deposit an anti-tack agent on the surface of these materials.